Isaiah 9:1 (King James Bible) and afterward did more grievously afflict her by the way of the sea
The 1830 typesetter replaced the original afterward with the more frequent form afterwards, probably unintentionally. The only other occurrence of afterward(s) in the Book of Mormon text ends in s (in Alma 13:19). Both forms occur in the King James Bible, with afterward favored over afterwards (66 versus 13 occurrences). For this Isaiah passage, the King James Bible reads afterward. The 1908 RLDS edition restored the original afterward, probably by reference to 𝓟.
Summary: Maintain in 2 Nephi 19:1 the adverbial form afterward, the reading of the original Book of Mormon text and also the King James Bible.